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A Comparative Study of DNA Complexation with Mg(II) and Ca(II) in Aqueous Solution: Major and Minor Grooves Bindings

Department of Chemistry-Biology, University of Québec at Trois-Riviéres, Trois-Riviéres, Québec G9A 5H7, Canada

Correspondence: Address reprint requests to H. A. Tajmir-Riahi, Tel.: 819-376-5052 ext. 3310; Fax: 819-376-5084; E-mail:tajmirri{at}uqtr.ca.

Although structural differences for the Mg-DNA and Ca-DNA complexes are provided in the solid state, such comparative study in aqueous solution has been less investigated. The aim of this study was to examine the bindings of Mg and Ca cations with calf thymus DNA in aqueous solution at physiological pH, using constant concentration of DNA (1.25 or 12.5 mM) and various concentrations of metal ions (2 µM–650 µM). Capillary electrophoresis, UV-visible, and Fourier transform infrared spectroscopic methods were used to determine the cation-binding modes, the binding constants, and DNA structural variations in aqueous solution. Direct Ca-PO₂ binding was evident by major spectral changes (shifting and splitting) of the backbone PO₂ asymmetric stretching at 1222 cm^-1 with K = 4.80 x 10⁵ M^-1, whereas an indirect Mg-phosphate interaction occurred (due to the lack of shifting and splitting of the phosphate band at 1222 cm^-1) with K = 5.6 x 10⁴ M^-1. The metal-base bindings were directly for the Mg with K = 3.20 x 10⁵ M^-1 and indirectly for the Ca cation with K = 3.0 x 10⁴ M^-1. Both major and minor groove bindings were observed with no alteration of the B-DNA conformation.